There are many applications where a power supply is called upon to provide multiple power supply rails for a system. Power supply rails are electrical connections that deliver separate current and voltages to the system. Different supply rails can have the same or different supply voltages. For example, power supply rails may power different chips or different blocks (circuits) in the same chip having different power requirements. Typically, different rails have different voltages and consume different amounts of power over time, depending on the behavior of the load circuitry. FIG. 1A shows an example of a system 100 that requires multiple supply rails. An application System on a Chip (SoC) 110 includes first cores 111 drawing 1.2V, second cores 112 drawing 0.6V, an analog-to-digital converter (ADC) 113 drawing 1.2V, and an input/output (I/O) device 114 drawing 1.8V. A radio frequency (RF) chip 120 requires power at 1.2V and 0.6V, a digital camera 130 requires 2.4V, and a digital display 140 requires 1.2V and 2.4V.
Individual DC-DC converters may be used to generate each of the required voltages separately. However, this may be economically inefficient because the power consumption of each block changes over time, as shown in FIG. 1B. The size and cost of a DC-DC converter is related to the maximum power that it is configured to deliver.
Another way to generate multiple rails is to use a single switched capacitor (SC) converter or a hybrid converter with SC conversion built in. FIGS. 2A-2D show single-input multi-output symmetric ladder SC converters. FIG. 2A is a circuit diagram of an SC converter drive having multiple output rails having voltage-stacking outputs. FIG. 2B is a circuit diagram of an SC converter drive having multiple output rails having non-stacking inputs. The current sources represent the load blocks that consume energy. Beyond the two examples in FIGS. 2A and 2B, the load blocks may be connected between any two of the rails, including VIN, VUPPER, VMID, VLOWER and Gnd. FIG. 2C is a circuit diagram of a drive implementation example of an SC converter. FIG. 2D is a diagram of an exemplary circuit using the SC converter to power the heterogeneous system in FIG. 1A. The symmetric ladder SC converter in FIG. 2C operates in a two-phase fashion, where the first phase is indicated by a dashed line, and the second phase is indicated by a dotted line. The symmetric ladder SC converter in FIG. 2C operates by alternating the first and second phase switches, closing the first phase switches and opening the second phase switches during the first phase, and closing the second phase switches and opening the first phase switches during the second phase. FIG. 2D shows the SC converter of FIG. 2C being used to power the heterogeneous system example in FIG. 1A. The switches may be controlled, for example by opening or closing based upon a received switching signal.
The level of supported power and conversion efficiency of an SC converter depends on the total capacitance used in the converter. However, previous SC converters have not addressed performance issues due to inadequate allocation of capacitance sources. Therefore, there is a need in the industry to address one or more of these deficiencies.